Cell separation using positive immunoselective techniques

Microfluidic Devices for Magnetic Separation of Biological Particles: A Review

Separation of microparticles and cells serves a critical step in many applications such as in biological analyses, food production, chemical processing, and medical diagnostics. Sorting on the microscale exhibits certain advantages in comparison with that on the macroscale as it requires minuscule sample or reagents volume and thus reduced analysis cycle time, smaller size of devices, and lower fabrication costs. Progresses have been made over time to improve the efficiency of these microscale particle manipulation techniques. Many different techniques have been used to attain accurate particle sorting and separation in a continuous manner on the microscale level, which can be categorized as either passive or active methods. Passive techniques achieve accurate manipulation of particles through their interaction with surrounding flow by carefully designed channel structures, without using external fields. As an alternative, active techniques utilize external fields (e.g., acoustic, electronic, optical, and magnetic field, etc.) to realize desired pattern of motion for particles with specific properties. Among numerous active methods for microfluidic particle sorting, the magnetic field has been widely used in biomedical and chemical applications to achieve mixing, focusing, and separating of reagents and bioparticles. This paper aims to provide a thorough review on the classic and most up-to-date magnetic sorting and separation techniques to manipulate microparticles including the discussions on the basic concept, working principle, experimental details, and device performance.

Past, Present, and Future of Affinity-based Cell Separation Technologies

Progress in cell purification technology is critical to increase the availability of viable cells for therapeutic, diagnostic, and research applications. A variety of techniques are now available for cell separation, ranging from non-affinity methods such as density gradient centrifugation, dielectrophoresis, and filtration, to affinity methods such as chromatography, two-phase partitioning, and magnetic-/fluorescence-assisted cell sorting. For clinical and analytical procedures that require highly purified cells, the choice of cell purification method is crucial, since every method offers a different balance between yield, purity, and bioactivity of the cell product. For most applications, the requisite purity is only achievable through affinity methods, owing to the high target specificity that they grant. In this review, we discuss past and current methods for developing cell-targeting affinity ligands and their application in cell purification, along with the benefits and challenges associated with different purification formats. We further present new technologies, like stimuli-responsive ligands and parallelized microfluidic devices, towards improving the viability and throughput of cell products for tissue engineering and regenerative medicine. Our comparative analysis provides guidance in the multifarious landscape of cell separation techniques and highlights new technologies that are poised to play a key role in the future of cell purification in clinical settings and the biotech industry. STATEMENT OF SIGNIFICANCE: Technologies for cell purification have served science, medicine, and industrial biotechnology and biomanufacturing for decades. This review presents a comprehensive survey of this field by highlighting the scope and relevance of all known methods for cell isolation, old and new alike. The first section covers the main classes of target cells and compares traditional non-affinity and affinity-based purification techniques, focusing on established ligands and chromatographic formats. The second section presents an excursus of affinity-based pseudo-chromatographic and non-chromatographic technologies, especially focusing on magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS). Finally, the third section presents an overview of new technologies and emerging trends, highlighting how the progress in chemical, material, and microfluidic sciences has opened new exciting avenues towards high-throughput and high-purity cell isolation processes. This review is designed to guide scientists and engineers in their choice of suitable cell purification techniques for research or bioprocessing needs.

Rapid Characterization of Magnetic Moment of Cells for Magnetic Separation

NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen were previously shown to be captured at high efficiencies by a microfabricated magnetic sifter. If fine control and optimization of the magnetic separation process is to be achieved, it is vital to be able to characterize the labeled cells' magnetic moment rapidly. We have thus adapted a rapid prototyping method to obtain the saturation magnetic moment of these cells. This method utilizes a cross-correlation algorithm to analyze the cells' motion in a simple fluidic channel to obtain their magnetophoretic velocity, and is effective even when the magnetic moments of cells are small. This rapid characterization is proven useful in optimizing our microfabricated magnetic sifter procedures for magnetic cell capture.

Effect of Magnetic Field Gradient on Effectiveness of the Magnetic Sifter for Cell Purification

In our experiments with NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen, we demonstrate capture efficiencies above 90% even at sample flow rates of 5 ml/h through our microfabricated magnetic sifter. We also improve the elution efficiencies from between 50% and 60% to close to 90% via optimization of the permanent magnet size and position used to magnetize the sifter. We then explain our observations via the use of finite element software for magnetic field and field gradient distributions, and a particle tracing algorithm, illustrating the impact of magnetic field gradients on the performance of the magnetic sifter. The high capture and elution efficiencies observed here is especially significant for magnetic separation of biologically interesting but rare moieties such as cancer stem cells for downstream analysis.

Induction and characterization of monoclonal anti-idiotypic antibodies to tick-borne encephalitis virus neutralizing antibody

Seven monoclonal anti-idiotypic antibodies (anti-ID MAbs, Ab2) were generated against virus-neutralizing and hemagglutination-inhibiting monoclonal antibody (Ab1) specific for tick-borne encephalitis (TBE) virus. Six of these anti-ID MAbs inhibited the binding of Ab1 to the virus antigen, thus classifying these anti-ID antibodies as Ab2 beta or AB2 gamma. Inhibition tests with heterologous anti-TBE sera revealed that these anti-ID MAbs were not recognized by anti-TBE antibodies and therefore they do not carry an internal image of TBE virus antigen. Hence, the anti-ID MAbs may be classified as Ab2 gamma type. None of the anti-ID MAbs induced production of antiviral antibodies nor protective immunity in syngeneic Balb/c mice. Using these anti-ID MAbs four nonoverlapping idiotopes were identified on Ab1 variable region.

Differentiation-related changes in quantitative binding of immunomagnetic beads

Experiments have been carried out to demonstrate that cell viability and phenotypic characteristics are not affected by exposure to constant magnetic fields or growth in the presence of Dynabeads. This paper also demonstrates that the changes in the surface concentration of the antigens, SSEA-1 (stage-specific embryonic antigen-1) and histocompatibility antigen (MHC H2-Db) during differentiation as determined by flow cytometric analysis, are mirrored by changes in the numbers of bound immunomagnetic particles (Dynabeads) targeted with monoclonal antibodies to these cell surface antigens. These results clearly indicate that the numbers of beads bound to cells reflect the numbers of specific surface antigens present on the cells.

Receptor-mediated cell attachment and detachment kinetics. II. Experimental model studies with the radial-flow detachment assay

Quantitative information regarding the kinetics of receptor-mediated cell adhesion to a ligand-coated surface are crucial for understanding the role of certain key parameters in many physiological and biotechnology-related processes. Here, we use the probabilistic attachment and detachment models developed in the preceding paper to interpret transient data from well-defined experiments. These data are obtained with a simple model cell system that consists of receptor-coated latex beads (prototype cells) and a Radial-Flow Detachment Assay (RFDA) using a ligand-coated glass disc. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine transient behavior with particles that possess fairly uniform properties that can be varied systematically, and the RFDA is designed for direct observation of adhesion to the ligand-coated glass surface over a range of shear stresses. Our experiments focus on the effects of surface shear stress, receptor density, and ligand density. These data provide a crucial test of the probabilistic framework. We show that these data can be explained with the probabilistic analyses, whereas they cannot be readily interpreted on the basis of a deterministic analysis. In addition, we examine transient data on cell adhesion reported from other assays, demonstrating the consistency of these data with the predictions of the probabilistic models.

Functional properties of CD19+ B lymphocytes positively selected from buffy coats by immunomagnetic separation

Here we report that human B lymphocytes can be positively selected directly from buffy coats applying the anti-CD19 antibody AB1 coupled to magnetic beads. This isolation protocol is highly efficient and the isolated cell population is of very high purity and viability. As judged by cell cycle analysis and various parameters for cell activation, the cells are still in a resting state after isolation. Furthermore, different functional assays have shown that the isolation procedure does not interfere with either activation or proliferation/differentiation of CD19 selected cells as compared to negatively isolated cells. As a consequence of cross-linking during the isolation process, the CD19 antigen is temporarily down-regulated as measured by AB1 binding. Despite this decreased expression, monoclonal antibodies to the CD19 antigen nevertheless inhibited anti-mu plus B cell growth factor induced B cell activation as reported also for negatively isolated cells. Taken together, the presented data strongly suggest that B cells isolated through the CD19 antigen can be used in critical functional assays.

The isolation of B lymphocytes from human peripheral blood using antibodies coupled to paramagnetic particles and rosetting techniques

A method is described for the complete removal of monocytes and a reduction of natural killer cells from a suspension of peripheral blood mononuclear leukocytes. The cells are depleted in a batch procedure employing monoclonal antibodies coupled to paramagnetic particles. The bound cells are removed with the help of a magnet. The resulting cell population, which contains less than 1% esterase positive cells and a fraction of the natural killer cells originally present, can be further depleted of T lymphocytes by erythrocyte-rosetting techniques.

Specific binding and release of cells from beads using cleavable tetrameric antibody complexes

A two-step separation procedure is described for the positive selection of cells based on their reactivity with mouse monoclonal antibodies. In the first step cells are specifically cross-linked to hapten-modified glass beads using tetrameric monoclonal antibody complexes. In the second step bound cells are selectively eluted by reductive cleavage of the tetrameric antibody complexes. The latter are comprised of two mouse IgG1 monoclonal antibodies (one recognizing a cell surface antigen on target cells and the other a hapten coupled to the glass beads) bound together by two F(ab')2 fragments of rat anti-mouse IgG1 monoclonal antibody. The complexes provide a specific cleavable cross-link between cell and bead because the disulfide bonds between the two Fab' arms of the F(ab')2 fragments can be broken under relatively mild conditions using dithiothreitol. This specific cleavage of the cross-linker allows elution of the specifically absorbed cells without co-elution of non-specifically bound cells. This is shown in the purification of CD3+ T cells from human peripheral blood, where the removed fractions were over 90% pure and approximately 50% of the positive cells were recovered. Separation of cells labelled with limiting amounts of tetrameric antibody complexes demonstrated that this separation technique was also effective for the purification of cells expressing low amounts of antigens. This was confirmed by the purification of CD34-positive cells from human bone marrow. With this approach, colony-forming cells were enriched 15-24-fold over density separated marrow.

L3T4 antigen expression by hemopoietic precursor cells

L3T4 (CD4) is expressed on immature hematopoietic cells. Sorting bone marrow cells on the basis of their expression of this antigen produces populations of cells that are markedly enriched for multipotential stem cells (CFU-s) and for myeloid precursors (CFU-c). We believe that L3T4 is transiently expressed by most, if not all, hematopoietic precursors early in their maturation. We suggest that the expression of CD4 molecules on the surface of immature precursors is required for their interaction with Ia bearing cells within the hemopoietic inductive microenvironment(s) of the marrow and thymus.

Immunoaffinity chromatography of lymphocyte subpopulations using tert-amine derived matrices with adsorbed antibodies

New polymeric solid-phase matrices for cell affinity chromatography were prepared and their advantageous characteristics compared with conventional matrices were highlighted. These new matrices are derivatives of poly(2-hydroxyethyl methacrylate) (PHEMA) containing a slight quantity of amino compounds as a co-monomer. They were applied to immunoaffinity selection between IgG+ and IgG- lymphocytes of the rat mesenteric lymph node. Simple physical adsorption was sufficient for anti-rat IgG antibodies to be immobilized on these matrices, allowing us to omit the laborious procedure of covalent-linking of antibodies on a matrix. As these matrices themselves showed extremely low non-specific adsorption of lymphocytes, a very dilute solution of antibody (0.02-0.08 mg/ml) was enough for column conditioning. This separation method gave IgG- lymphocytes of more than 90% purity and almost 95% yield within as short a time as 7 min. Further, IgG+ lymphocytes were obtained in good yield (80-90% of loaded number) by recovering the adsorbing cell fraction from the column by gentle pipetting of the matrix.

Quantitative flow cytometric and clonogenic evaluation of glass bead affinity fractionation of antibody-labeled murine bone marrow

Monoclonal antibodies and a glass bead affinity fractionation technique were used to selectively deplete subpopulations of murine bone marrow cells. Flow cytometric analyses permitted quantitative measurement of subpopulation depletion and characterization (light scatter and fluorescence intensity) of both the eluted and bound cell subpopulations. Mouse bone marrow cells were labeled with selected monoclonal rat anti-mouse antibodies directed against cell surface antigens and were eluted through a glass bead column coated with goat anti-rat immunoglobulin. Unlabeled cells passed through the column, whereas cells labeled with the antibody were selectively retained. Column operating conditions for optimal depletion of labeled cells were determined. With specific column conditions, 97% of the antibody positive cells were retained on the column. In addition, clonogenic assays on cells sorted from unfractionated and column fractionated preparations provided estimates of the fraction of granulocyte macrophage progenitors (CFU-GM) in the different cell subpopulations. The enrichment of CFU-GM achieved in the eluted cell populations was dependent upon the antibody used for cell labeling and ranged from four- to six-fold. Since large numbers of cells can be processed rapidly, this technique, in combination with antibodies specific for non-clonogenic cells, is particularly suitable when preparations enriched in colony-forming progenitors are required.

Experimental strategies for the study of cellular immunity in renal disease

This overview has examined some of the current experimental options available for the study of cellular immunity in the immunopathogenesis of renal disease. T cell immunity, where it has been examined, seems to have a particularly pivotal role in orchestrating and regulating functional patterns of renal injury. The use of the research methods presented here for the study of cell-mediated interactional events in kidney disease, however, has lagged behind similar efforts in other organ systems. We hope, therefore, this report will serve to stimulate and strengthen further interest in the cell biology of the nephritogenic immune response.

Positive selection of viable cell populations using avidin-biotin immunoadsorption

We have developed a new method for the selective enrichment of lymphoid subpopulations from dog and human bone marrow and peripheral blood. A mononuclear cell preparation was treated successively with monoclonal antibody, biotinylated goat anti-mouse immunoglobulin and passed over a column containing avidin linked to polyacrylamide or Sepharose beads. Adherent cells were recovered by mechanical agitation and analyzed by immunofluorescence staining and fluorescence-activated cell sorter analysis. Dog bone marrow mononuclear cells were treated successively with the antibody 7.2, which recognizes the Ia-antigen, 1:500 dilution of biotinylated goat anti-mouse immunoglobulin and passed over avidin-Biogel (1 mg/ml) at a flow rate of 3.0 ml/min. Enrichment from a starting population that was 24.4 +/- 9.1% 7.2-positive to 78.3 +/- 6.8% 7.2-positive adherent cell population was observed with 47.7 +/- 7.8% recovery of 7.2-positive cells. Human bone marrow mononuclear cells were treated successively with the T cell antibody Leu-4 followed by 1:500 dilution of B-GAMIg and passed over a column of avidin-Biogel (1 mg/ml) at a flow rate of 1.5 ml/min. Enrichment from 7.2 +/- 3.3% Leu-4-positive cells in the starting cell population to 73.1 +/- 6.8% Leu-4-positive cells in the adherent cell population with total recovery of Leu-4-positive cells averaging 64.0 +/- 12.7%. Human bone marrow mononuclear cells positively selected with antibody Leu-4 or another T cell antibody, Leu-5 had a markedly enhanced response to the T cell mitogen, phytohemagglutinin compared to untreated bone marrow. Enrichment of a subpopulation of lymphocytes from dog peripheral blood mononuclear cells has been accomplished using antibody DT2, which reacts with a broad spectrum of dog lymphocytes. Nonspecific cell binding is primarily limited to granulocytes and monocytes. Future work is being directed at improving recovery of positively selected cells, reducing nonspecific cell binding and applying the technique to the selective enrichment of hematopoietic stem cells from bone marrow.

A fractionation procedure of mouse bone marrow cells yielding exclusively pluripotent stem cells and committed progenitors

The cell surface phenotype of pluripotent hemopoietic stem cells (CFU-S) and committed progenitors (CFU-C1, CFU-C2, BFU-E) of mouse bone marrow was analyzed with respect to their binding of wheat germ agglutinin (WGA) and two monoclonal antibodies, anti-GM-1.2 and anti-PGP-1. Stained cells were fractionated on the basis of differences in fluorescence and light scatter intensity using a light-activated cell sorter. The 6% of the cells that bound most WGA and that also had a relatively high forward light scatter (FLS) and low perpendicular light scatter (PLS) contained nearly all stem cells (CFU-S) and progenitors. Anti-GM-1.2 stained only mature myeloid cells, not CFU-S or the in vitro colony-forming cells. Anti-PGP-1 stained all bone marrow cells in varying intensities: lymphoid cells were dull, CFU-S were intermediate, CFU-C2 were brighter, and mature myeloid cells very bright. Enrichment of progenitor cells was performed by a two-step sorting procedure. First, the 6% most WGA-binding cells with high FLS and low PLS were sorted out. A 10-15-fold enrichment of progenitors and CFU-S was obtained. Next, these cells were restained with anti-GM-1.2 or anti-PGP-1 and again fractionated on the FACS. The GM-1.2-negative cells were then another four- to sevenfold more enriched for stem cells and progenitors. Of the cells in this fraction, 95% could be assigned to a colony-forming unit. With anti-PGP-1, CFU-C2 could be partly separated from more early cells such as CFU-S and BFU-E.

Isolation of pure functionally active CD8+ T cells. Positive selection with monoclonal antibodies directly conjugated to monosized magnetic microspheres

A monoclonal antibody of the IgM isotype, ITI-5C2, which binds with high affinity to CD8 molecules, was directly conjugated to the monosized magnetic microspheres M-450. This permits selective removal of the CD8+ T cell subset (T8) from peripheral blood mononuclear cell suspensions in a rapid one-step procedure. With a low ratio of microspheres to cells (2:1), functionally active T8 cells can be recovered. In vitro experiments involving such positively selected T8 cells or recombinations of isolated T8 and T4 subsets, demonstrate that the presence of M-450 microspheres coated with ITI-5C2 do not interfere with the immunological functions of the positively selected cells. The method has possible application in the isolation of all cell populations where high avidity mAbs of appropriate specificity are available.

Separation of lymphocyte subpopulations using biotin-avidin erythrocyte rosettes

The major method for isolating murine lymphocyte subpopulations involves negative selection using antibody plus complement-mediated cytolysis. We have developed an efficient rosette method for enriching murine B and T cells using biotin-conjugated antibodies and avidin-coated sheep erythrocytes. Rosetted and non-rosetted subpopulations are separated rapidly on Percoll cushions. In systems employing rabbit anti-mouse immunoglobulin or monoclonal rat anti-mouse Thy-1.2 conjugated to biotin, positively-selected cells are greater than 90% pure while negatively-depleted populations possess less than 2% contamination with unwanted cells. Recoveries from starting spleen cell populations range between 50 and 75%. This method provides an easily performed alternative for obtaining positively and negatively selected cell populations and can be used with any biotin-conjugated antibody protein.

Characterization of monoclonal antibodies to rabbit renal cortical cells

The immunological heterogeneity of the rabbit nephron was investigated using monoclonal antibodies. Seventeen antibodies have been produced by fusion of NS1 myeloma cells with spleen cells from BALB/c mice immunized with unfractionated rabbit renal cortical cell preparations. Sixteen antibodies reacted with proximal tubular cells: 11 with the brush border and 5 with basolateral membrane or intracytoplasmic components. Only one of the latter was specific for constituents of the proximal tubule. One antibody reacted with the cortical collecting tubule. Eight of the anti-brush-border antibodies were further characterized by immunoprecipitation of detergent-solubilized radiolabeled brush-border membrane vesicles. Seven proteins with subunits ranging in molecular weight from 90,000 to greater than 340,000 were identified. Systematic survey showed that one of these proteins with a subunit molecular weight of 115,000 exhibited leucine aminopeptidase activity. Selected monoclonal antibodies bound to Sepharose 4B immunoadsorbents were used to deplete solubilized brush-border membrane vesicles of a given antigen and to identify leucine aminopeptidase. Furthermore, the obtention of specific antibodies directed against the proximal tubule allowed us to set up a simple method for renal cell separation: isolated renal cortical cells could be depleted by 80% in proximal cells by passage over columns of Sepharose 6MB covalently linked with three different monoclonal anti-brush-border antibodies, thus leading to cell suspensions considerably enriched in tubule cells originating from the more distal segments of the nephron.

Characterization of effector cells in lymphocytotoxicity to autologous hepatocytes in HBsAg-positive and autoimmune chronic active hepatitis (CAH)

Peripheral blood lymphocyte subsets involved in cytotoxicity to autologous hepatocytes have been characterized by isolation on antibody-coated Petri dishes in autoimmune and HBsAg-positive chronic active hepatitis (CAH). In autoimmune CAH and in HBsAg-positive CAH without HBcAg in liver tissue, cytotoxicity is sustained by non-T lymphocytes and is confined to M1-positive cells bearing Fc receptors: M1 cytotoxicity inhibition by adding aggregated IgG suggests that these cells are responsible for an antibody-dependent cell-mediated mechanism (ADCC). Moreover, when T-enriched fractions were separated in T4, T8 and 5/9 positive subsets, only the first one showed a significant cytotoxicity: T4 positive cells might act as cytotoxic T cells or might be involved in delayed type hypersensitivity (DTH) reactions. Cytotoxic T lymphocytes in HBsAg-positive CAH with HBcAg in liver tissue are confined in T8 positive subset, while helper/inducer T cells (T4 positive or 5/9 positive) seem to play an important role only in the induction of cell-mediated injury against hepatocytes. The inhibition of T cell-cytotoxicity by preincubating liver cells with monoclonal antibody (Mab) anti-HLA AB and not with Mab anti-HLA DR or aggregated IgG supports the involvement of the class I major histocompatibility complex (MHC) expressed on the hepatocyte surface.

Preparative scale separation of functionally distinct murine B cell subpopulations

Mouse splenic B cells were found to be rapidly and reproducibly fractionated by adherence at 4 degrees C to plastic dishes pretreated with an alkaline buffer. The cell subsets obtained exhibited marked differences in size, surface immunoglobulins (sIg), and responses to B mitogens. Adherent B lymphocytes, bearing high densities of sIg, responded particularly to LPS whereas non-adherent B lymphocytes, with low densities of sIg, responded especially to dextran sulfate. The correlations between the separated populations and subsets at distinct maturation stages are discussed.

DNA-mediated transfer of human melanoma cell surface glycoprotein gp130: identification of transfectants by erythrocyte rosetting

DNA sequences encoding a human melanoma membrane-bound sialoglycoprotein of 130,000 molecular weight (gp130) were introduced into a clonal derivative of mouse B-16 melanoma cells with the selectable neomycin resistance gene (aminoglycoside phosphotransferase). Mouse transfectants were identified by a rapid and precise screening method with mouse monoclonal antibodies and erythrocyte rosetting. The frequency of gp130 transfectants was approximately 1 in 2,000 to 5,000 colonies with neo+ cells. Analysis of secondary mouse transfectants has revealed that the transfected gp130 has a molecular weight, isoelectric point, intracellular processing, peptide map, and spatial orientation of surface-exposed epitopes indistinguishable from those seen with gp130 from human melanoma cells. In contrast to primary transfectants, secondary transfectants expressing gp130 lack demonstrable human repetitive sequences.

DNA-mediated transfer of human melanoma cell surface glycoprotein gp130: identification of transfectants by erythrocyte rosetting

DNA sequences encoding a human melanoma membrane-bound sialoglycoprotein of 130,000 molecular weight (gp130) were introduced into a clonal derivative of mouse B-16 melanoma cells with the selectable neomycin resistance gene (aminoglycoside phosphotransferase). Mouse transfectants were identified by a rapid and precise screening method with mouse monoclonal antibodies and erythrocyte rosetting. The frequency of gp130 transfectants was approximately 1 in 2,000 to 5,000 colonies with neo+ cells. Analysis of secondary mouse transfectants has revealed that the transfected gp130 has a molecular weight, isoelectric point, intracellular processing, peptide map, and spatial orientation of surface-exposed epitopes indistinguishable from those seen with gp130 from human melanoma cells. In contrast to primary transfectants, secondary transfectants expressing gp130 lack demonstrable human repetitive sequences.

Dual-parameter scatter-flow immunofluorescence analysis of Bacillus spores

Using a commercial flow cytometer (Cyto-fluorograf), narrow-forward-angle (NFA) light-scatter signals were detected for spore preparations of Bacillus anthracis Vollum, B. anthracis Sterne, B. cereus NCTC 8035, and B. subtilis var niger. In the flow immunofluorescence (FIF) analysis of spores stained with fluorescein-conjugated hyperimmune antibody to B. anthracis Vollum spores, fluorescence histograms could be acquired by selecting on NFA scatter. Fluorescence data selected on ninety degree scatter were rather noisier. Fluorescence analysis by dual parameter NFA scatter-FIF techniques was shown to have several advantages over the subtraction FIF method reported earlier. The implication from FIF analysis of spore suspensions and corresponding cell-free supernatants that the peak in the fluorescence histogram was caused by signals from fluorescing spores, was confirmed by use of the cell sorter and subsequent microscopy of the sorted samples. Although a proportion of spore aggregates was present in samples sorted from the right-hand tail of the fluorescence histogram, it was demonstrated that the majority of the observed distribution of fluorescence was not due to the formation of aggregates but was rather an expression of variation in the degree of staining of individual spores.

Immunological approaches to the nervous system

Immunology has had a major impact on neurobiology, expanding dramatically the number of subjects amenable to investigation. Studies with antibodies to neuropeptides, transmitters, and transmitter enzymes have disclosed a great heterogeneity among neurons and have provided clues for interpreting anatomical connections. Monoclonal antibodies are being used to identify functionally related subpopulations of neurons and cell lineages in development and to study mechanisms by which axons grow along stereotypic pathways to reach their targets. Other antibodies have identified molecules that appear to participate in cell aggregation, cell migration, cell position, and axon growth. Antibodies have revealed that many proteins are concentrated in anatomically distinct regions of the neuron. Moreover, these studies have suggested that individual proteins have different antigenic epitopes shielded or modified in different parts of the same neuron. Antibodies to membrane proteins crucial for neuronal function, such as ion pumps, ion-selective channels, and receptors, have been used to map their distributions and to study their structures at high resolution.

A simple method for immunoselective cell separation with the avidin-biotin system

A new method for immunoselective cell separation is described which uses biotinylated antibodies and avidin-coupled sheep erythrocytes for rosette formation, and a density gradient to separate the rosetting from the non-rosetting cells. The utility of the technique is illustrated by separating subpopulations of rabbit, mouse and rat lymphocytes. The method offers a rapid, sensitive and easily reproducible means for obtaining purified cell populations.

Immune dysfunction in diabetes-prone BB rats. Interleukin 2 production and other mitogen-induced responses are suppressed by activated macrophages

Spleen cells of diabetes-prone BB Wistar rats were found to generate excessively low proliferative responses, and interleukin 2 (IL-2) levels in response to T-dependent mitogens. This abnormality was not due solely to abnormal T cell numbers since: (a) addition of BB spleen cells of BB splenic macrophages to normal major histocompatibility complex (MHC)-matched Wistar Furth (WF) spleen cells resulted in severe suppression of concanavalin A (Con A)-, phytohemagglutinin (PHA)-, and pokeweed mitogen (PWM)-mediated proliferation, and IL-2 production; (b) macrophage depletion from BB spleen cells, but not B cell or T cell depletion, removed completely the suppressive effects of BB cells on WF cells; (c) macrophage depletion greatly enhanced the response of BB lymphocytes to T-dependent mitogens. Although suppressor macrophages could also be found in the spleen of WF control rats they were present in much smaller numbers than in the spleen of BB rats. The suppressive effect of BB macrophages was partially reduced by addition of the prostaglandin synthetase inhibitor indomethacin to cultures. Furthermore, indomethacin (but not catalase or PMA) considerably augmented IL-2 secretion of Con A-stimulated BB spleen cells, but had little effect on WF spleen cells. In contrast, prostaglandins E1 and E2 (PGE1 and PGE2) suppressed IL-2 production. While IL-2 secretion was severely depressed in BB rats unstimulated and lipopolysaccharide (LPS)-stimulated IL-1 secretion by splenic macrophages was normal. BB macrophages did not inactivate IL-2. Low IL-2 production and macrophage-mediated suppression were features of all BB rats tested.

Cell separation: a review

This review summarizes currently available techniques for cell separation. Techniques that exploit differences in physical properties of cells are widely used but have a number of limitations. Those that are based on differences in surface properties may more readily permit reproducible separation of a functionally homogeneous population of cells. Unfortunately very few techniques achieve separation of cells on the basis of differences in their functional characteristics.